I agree with Andrew *and* Michael and, hopefully, with Paul and Allin.

Only concrete labour time and market prices are observable magnitudes. Even
the calculation of prices of production involves strong assumptions,
especially averaging out market prices over long periods *and* somehow
calculating the impact of technical progress and the changes in the quality
of the goods. This exercise necessarily involves some degree of
arbitrariness, as Michael explains very clearly in his papers.

Within production, average techniques of production can be inferred if the
actual techniques are averaged out, but the problems are similar to those
listed above.

It is even worse with labour; the reduction of skilled labour to uniform
abstract labour is terribly difficult (for reasons brilliantly explained by
Philip Harvey in his 1985 RRPE paper). Averaging out concrete labours, as in
I-O tables, simply will not do because the skills will remain different - as
in hours of ditch-digging and computer programming, which create different
quantities of value.

In my opinion, these difficulties *prevent* the calculation of prices of
production from the technologies of production (however we may conceptualise
the wage rate). Yet *this is not a problem at all*, because there is no
reason why one should entertain this possibility or have any interest in this
exercise, for the reasons that Andy explains - namely, value is a social
relation which expresses the mode of production under capitalism, and price
is its form of appearance. There is no other form of apperance of value but
price.

The attempt to calculate production prices from I-O tables seems to me to
reflect a certain dissatisfaction with this fact (ie, that price is the form
of value, and value is social labour), as if we wanted calculate the price
vector just to make sure that our concept of value is, somehow, 'right'. The
point is that value is not hidden within commodity prices, and does not need
to be 'found'. Value is visible, but only - I stress the word only - through
price.